Telephone receiver



Oct. 9,- 1928.

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i .UNITED STA PATENT o-FFicE.-

WARREN c. JONES, or ELUSHING,'NEW' YoRx,Ass1GNoR'ro :anniJ vTELEPHONE LABORATORIES, INCORPORATED, OE -NEW YORK, N. Y., A CORPORATION 0E NEW YORK.

- TELEPHONE micEIvnR;A

Appiieftion mea member-3i, 192s. semi No. 158,186.

'. This invention relates vto receivers and par tic'ularly to vreceivers which 4employ a p ermanent magnet for. supplying polarizing" iiux.

An objectvof this invention is to obtain increased and substantially constant eiciency in a telephone receiver.

'In a telephone receiver for use in sub-.

scribers'sets, increased etliciency is of great importance in-that each .transmission unit gain in receiver eiiicie'ncy makes possiblean increase'of approximately one mileV in the I length of the ,subscribers loop whichcanfbe e1nployed. `It-is of advantage, moreover, that the maximum eiiiciency of the receiver should occur at as low a value of polarizing iiux as is consistent .with quality, since this malrcs possible a reduction in the size ot the perf.

' preferably of aluminum, having a base porf manent magnet used. .In accordance with this invention, the eiiiciency ot' a permanent magnet receiver is increased by'employing a high permeability material in its magnetic circuit. This increased eiiiciency is realized, moreover, at a low value of polarizing iux, thus making possible a decrease in V'the size of the permanent magnet employed. The.'eicicncy of this receiver is maintained at its maximum value by' constructing the permanent magnet ot' a` material possessing .high coercivity. j

1n one aspect, this invention may be considered asan improvement on the receiver disclosedV in Patent #1,551,143 ot' August- 25, 1925, to. H. A. Frederick. l

The invention may be better understood by referring to the following description and. l the accompanying drawing in which Fig. 1 shows a telephone handset in which a. receiver, -in accordance with the present invention, may be employed;

Figf2 is an enlarged sectional view taken through the center. of the receiver portion of the handset shown in Fig.'1;

Fig. .3 shows, by means of curves, the relative efficiency Qt a receiver constructed accordance with this invention and o ta similar type of receiver employed heretofore; Fig. 4 shows the relationexjsting between polarizing magnetomotive force and polarizing flux density in the air'gapsof the mag- A vnetic circuitof thereceivers whose efficiency curves are shown in Fig. '3

Fig. 5 showsthe relationbetween polarizf i densi-ty, inthe air gaps of these receivers, re-

sulting from alternating current flowing in the receiver winding; Fig. (5 shows the relation between polarizmg-magnetomotive force and .the product of "the polarizing and Variable fluX'densities plotted in the curves of Figs.-'4 and 5; and

Fig. 7 shows the relation between demagnetizing force and transmission loss for ref ceiv'ers employing different materials in theirrespective lpermanent magnets.

. et'erring now to the drawing, Fig.f1 shows a telephone handset, comprising a handle 10, a transmitter 11, and a receiver 12 constructed in accordance vwith thisA invention. i

FiO'. 2 is a cross-sectional viewl showing the receiver 12 and a. portion of thehandle 10 in detail.' The Yreceiver consists ot a casing,

tion 13 for supporting the magnetic structure of the receiver. This casing is provided with externally threaded portions 14, 15 and 16 ofdiii'erent diameters, respectively. The

portion 14 is adapted to be threaded into anv internally threaded ring 40 embedded in the handle 10, thereceiver capor ear piece 35 is fitted onto the threaded portion 16, and a lock nut 17, in the form of a ring prefera- `bly of phenol-plastic composition, engages the threaded portion 15 and is adapted to be V"screwed against a bearing portion of the are mounted ont-he cores 36, vand one end otl the coil: winding` is connected to the metallic strip 21 secured to the' insulating inember 22, this member being'securedfto the base portion 1 3 by' the screws 23. The other endjof the `metallicstrip is connectedelectrically to the spring 24, secured vto the insulating member 22. 'boss 37 on the lower portion-of spring 24 is adapted to make a firm contact with a contact member 41 secured'within the handle 10 and connected electrically to agconductor 42 in the handle of the handset struct-ure. The

the metallic casing 13. A diaphragm 25 of magnetic'm'aterial is clamped between the upper portion of the aluminum casing and lthe receiver cap 35. In some cases, vit may be preferable, however, to emploi' a dia.- phraglnof non-magnetic material aving a other endof the'coil winding isgroundedto piece of magnetic material attached thereto. The magnetic material employed in the diaphragm 25 and the pole pieces 36 is preferably one having an effective permeability, at

low magnetizing forces, very much higher than that of silicon steel, a lower hysteresis loss and a resistivity of the order of 45 microhms per centimeter cube. An alloy composed of 45% nickel and 55% ironhas such properties when suitably heat treated. To obtain this material, iron and nickel are fused together, preferably in the proportions of 55% iron and 45% nickel, good commercial grades of these materials being suitable for this purpose. The molten composition is then poured into a mold and cooled either in the form in which it is to be employed or in a convenient form to be worked over for this purpose. While 55% iron and 45% nickel have been mentioned as being the proportions of the ingredients of nickel and iron preferably to be employed in making up this material, it should be understood that this proportion may deviate'from these figures and` under certain conditions, it may even be desirable to add a third element. Thus, for example, if the composition consists of 211/z per cent iron and. 781/2 nickel, a material having even higher permeability than that of the 55% iron-45%` nickel composition is obta-ined, but this latter composition has a considerably lower resistivity. By the addition of` approximately 1% chromium to the 211/2% iron-781/2% nickel' composition, the resistivity is increased to approximately that obtained with the 55% iron-45% nickel composition. Fora detailed description of vari-- ous compositions of nickel and iron and other elements which may be used reference is made to patent to Gr. W. Elmen #1,586,884, June 1, 1926. 1

To develop the utmost permeability of the magnetic material, the finished parts are subjected to a heat treatment which, for particular cases, varies somewhat as regards the temperatures employed and the duration of the 'heating and cooling periods. The optimum values of vthese periods can readily be determined for a specific case by experiment.

In the case o-f the preferred composition con-l sisting of 55% iron-45% nickel, a suitable heat treatment has been found to be to heat the material to a temperature of 11.00 C. and then to cool at the rate of approximately 4 C. per minute. This rate of cooling is not critical, but can be varied over wide limits.

The magnetic material obtained in this manner has an extremely high effective permeability at low magnetizing forces and saturates at a point lower than the saturation point of silicon steel.

The permanent magnet 30 is preferably constructed of cobalt steel which has a considerably higher coercive force than tungsten steel, although other materials having high coercive force may be employed. One suitable form of cobalt steel alloy consists of 20% cobalt, 8.5% tungsten, 1.6% chromium, 0.66% carbon and the rest iron. Other suitable cobalt alloys are disclosed in United States patents to Honda, 1,338,132 and 1,338,133, April 27, 1920.

Fig. 3 shows efiiciency curves for a receiver constructed in accordance with the present invention (curve a) andlfor a similarly constructed receiver employing a ferro-type diaphragm, silicon steel'cores and a permanent magnet of tungsten steel (curve b). In obtaining these curves, a direct current was caused to flow in the receiver winding, in either direction so as to add to or subtractfrom the polarizing flux generated by the permanent magnet. The polarizing ma'gnetomotive force is plotted in ampere turns above an arbitrary zero value and the transmission gain is plotted in transmission units above or below the maxiinum efficiency indicated in curve b. The curves show that when the permanent magnet is designed to provide the polarizing flux necessary for maximum eiiciency, a receiver constructed in accordance with this invention, affords a transmission gain of about three transmission units over .the one employing a to the receiver constructed in accordance with' this invention are designated by the letter a while the curves for the other receiver referred to above, namely onel employing a ferro-type diaphragm, and silicon steel cores, are designated by the letter-b. In'obtaining these curves the core pieces were attached to the poles of an electromagnet and the olarizing flux and variable fiux were me sured over a range of polarizing magnetomotive forces by means of searchl coils introduced in the magnetic circuitl at the pole tips. 4The curves `of Fig. 4 indicate the relation between polarizing magnetomotive force and polarizing flux'density iii-the magnetic .circuits of these receivers, and the curves the relation between polarizing magnetomotive force and variablev fiux density. Tlieuseful force exerted onthe'diaphragm of a receiver is a function of the product of the polarizing and variable flux densities plotted in Fig. 6. The curves of Fig. 6 show the relation between polarizing magnetomotive'force and the product of the polarizing and variable flux densities plotted in Figs. 4 and 5, respectively. As sliown in this figure the maximum. value of the product, for the receiver employing'nickle-iron alloy in its magnetic circuit llU of rig. 5 Show is approximately 65% higher than the maximum value for .the receiver employing the ferro-type Idiaphragm and the silicon steel cores. This improvement in the force exerted on the diaphragm is mainly responsible for the increased efficiency of the receiver of this invention as sho Wn in Fig. 3. A

The curves of Fig. 7 show the transmission loss due to demagnetization of t-he permanent magnets of two receivers; the receiver. t0 which curve a relates employs a permanent magnet of cobalt steel While the'one to' Which curve b relates, employs appermanent ma net of tungsten steel. `It is apparent from t ese curves that not only is greater stability obtained in the receiver employing the cobalt steel magnet but also that the losses in. etticiency resulting from demagnetization in the case of thetungsten steel magnet may entirely ofset'the improvement obtained by the use of the nickel-iron alloy in the magnetic circuit of the receiver in accordance with` this invention. In order to maintain the receiver at its maximum efficiency, therefore, it is necessary'v to employ a permanent magnet having a high coercive force.

What is claimed is :A

1. A telephone receiver comprising a' permanent magnet of cobalt steel and pole pieces for said magnet composed of an alloy in g chiefiy of nickel and iron.

2. A telephone receiver according to the preceding claim in 'which the nickel component is less than 50% of the Whole.

3. A receiver comprising a Winding and a magentic circuit therefor including a diaconsist-- phragm and a permanent magnet, said diaphragm being formed of a material comprising nickel and iron, having a permeability greater than that of silicon steel at low magnetizing forces and said magnet being formed of a cobalt steel alloy having a coercive force greater than thatof tungsten steel.

4. A receiver comprising a permanent magnet of cobalt steel, pole pieces for said magnet composed of nickel-iron alloy, and a diaphragm of nickel-iron alloy mounted in operative relation to said pole pieces.

5.v A receiver comprising a IWinding and a winding associated with'said pole pieces, said tliaphragm and pole pieces being composed of a material comprising nickel and iron having a. permeability higher than that of silicon steel at low magnetizing forces and a saturation point below that of silicon steel.

In witness whereof, I hereunto subscribe my name this 29th day of December A.

WARREN C. JONES. 

